A component of the hierarchical structure defined by the document type definition; it is identified in a document instance by descriptive markup, usually a start-tag and an end-tag.

HTML

HyperText Markup Language.

HTTP

A generic stateless object-oriented protocol, which may be used for
many similar tasks by extending the commands, or "methods", used. For
example, you might use HTTP for name servers and distributed
object-oriented systems, With HTTP, the negotiation of data
representation allows systems to be built independent of the development
of new representations. For more information see:
http://www.w3.org/hypertext/WWW/Protocols/Overview.html

markup

Text added to the data of a document to convey information about it. There are four different kinds of markup: descriptive markup (tags), references, markup declarations, and processing instructions.